In recent years, high integration of semiconductor devices progresses with high performance of semiconductor devices, and the demand of fine wiring patterns is increasing. The wiring rule on the order of 0.13 to 0.10 micrometers or less is under development. And, aluminum (Al) as the conventional wiring material has been substituted for by copper (Cu) which has a low resistance with little influence of wiring delay.
Therefore, the combination of the Cu film formation technology and the fine wiring technology serves as an important key technology for the multilevel interconnection technology in recent years.
The sputtering method, the CVD method, the plating method, etc. are generally known as the above mentioned method for film deposition of Cu. However, when taking into consideration the fine wiring technology, each method has a limited coverage, and it is very difficult to form a Cu film efficiently in a fine pattern which is at a high aspect ratio of 0.1 micrometer or less.
Then, as a method of efficiently forming a Cu film in a fine pattern, a method for film deposition of Cu using a medium of a supercritical state is proposed (see “Deposition of Conformal Copper and Nickel Films from Supercritical Carbon Dioxide”, SCIENCE vol. 294, Oct. 5, 2001, www.sciencemag.org).
According to the literature “Deposition of Conformal Copper and Nickel Films from Supercritical Carbon Dioxide”, a Cu film formation precursor compound (precursor) which contains Cu is dissolved using CO2 of a supercritical state, and a Cu film is formed.
The term “supercritical state” means that the substance concerned is in the state of having the features of a gas and a liquid, when the temperature and pressure of the substance concerned become beyond a value (critical point) peculiar to the substance concerned.
For example, in the above-mentioned medium using CO2 of the supercritical state, the Cu film formation precursor which is the precursor compound containing Cu has a high solubility but has a low viscosity and a high diffusibility, and the Cu film formation is attained in a fine wiring pattern of a high aspect ratio.
The embedding of Cu to a fine pattern is introduced in the above literature “Deposition of Conformal Copper and Nickel Films from Supercritical Carbon Dioxide”.
However, when actually creating a semiconductor device by the above-mentioned Cu film formation, it is necessary to form the diffusion preventing film of Cu between Cu and an insulating layer, in order to prevent diffusion of Cu to the inside of the insulating layer between the Cu wirings, for example.
It is known that any of a metal film, a metal nitride film or a laminated film of a metal film and a metal nitride film may be used as the Cu diffusion preventing film, and the metal is chosen from a group including Ti, Ta, W, TiN, TaN, WN, etc.
The sputtering method has been conventionally used for formation of the above-mentioned Cu diffusion preventing film. However, it is difficult to provide a sufficient coverage for a fine pattern of the recent semiconductor devices, and the sputtering method has such difficulty.
In recent years, the CVD method which provides a good coverage has been used in many cases instead of the sputtering method. However, the current situation is that if it is applied to a fine pattern of a high aspect ratio of 0.1 micrometers or less, the coverage of the CVD method is also inadequate.
Moreover, when formation of a Cu film using the medium of a supercritical state is considered, a decompression process is required in addition to a pressurization process for the sputtering method or the CVD method, and it is necessary to prepare two kinds of devices with different configurations. Further, it is necessary to convey a substrate between a pressure reduction device and a pressurization device, and there is a problem that the productivity is low.